Occurrence of Melampsora rusts in biomass willow plantations for renewableenergy in the United Kingdom

The natural occurrence of Melampsora rusts in biomass willow plantations fo r renewable energy was investigated at four sites in the UK during 1992-199 4. Three sites, located at Long Ashton, south west England, Loughgall, Nort hern Ireland, and Craibstone, Scotland, were rust/clone trials that contain ed standard 24 willow clones and the fourth site at Markington, northern En gland, had a similar range of willows. Larch-alternating M. epitea (M. lari ciepitea) was found to be most prevalent. Melampsora capraearum was predomi nant on S. caprea hybrids and the stem-infecting form occurred mainly on S. viminalis 'Bowles Hybrid'. To identify different pathotypes in larch-alter nating M. epitea, field rust samples were tested for pathogenicity in the l aboratory using eight willow differentials. A total of 12 pathotypes were i dentified. More pathotypes were found at Long Ashton, Loughgall and Marking ton, where extensive, long-term willow plantings were grown, than at Craibs tone, where the planting was more isolated. A major breakdown of rust resis tance in S. x mollissima 'Q83' in the UK in 1992 was caused by the emergenc e of a new pathotype. Our results also suggest that the larch-alternating M . epitea found in UK biomass willow plantations may consist of genetically separate populations. This would provide an opportunity to plant willow clo nes that harbour different mating populations, in mixed plantations in orde r to enhance the property of mixtures to suppress rust. (C) 1999 Elsevier S cience Ltd. All rights reserved.